The invention relates to a method for measuring the light tightness of a piston ring that is provided with a joint and created so as to be non-round.
DD 148 982 B1 discloses a measuring system for determining impermissible gaps between rotation-symmetrical components, in particular for checking the sealing gaps of piston rings, using a light source and a photoreceiver. The piston ring to be checked is clamped into a ring gauge, and the optical axis of a pulsed light source is directed at the gap between the piston ring and the ring gauge by means of an interposed lens system, wherein a test receiver is disposed opposite the gap in the optical axis, the analog electrical signal of the test receiver, which is dependent on the gap width, being supplied to a selective amplifier, wherein it is possible, by means of a known electronic circuit, to retrieve, store and display the analog electrical signals that are detected over the course of a rotation of the ring gauge based on the circumference.
A method for ascertaining the shape-conforming capability of piston rings in a non-round cylinder liner became known from DE 100 30 368 A1. For this purpose, a dimensionally stable test liner is provided and accommodated in a shape testing device. The inner surface of the test liner is provided with an exactly circular cylindrical section corresponding to the nominal diameter of the piston ring and, axially adjoining, with a slight non-round section having four curved convexities of approximately 20 μm. The cross-sectional surface enclosed by an inscribable circle and by the convexities is used as a reference surface. The profile progression of the inner surface of the piston ring over the non-round section circumference is ascertained by way of conventional shape measurement of the piston ring that is inserted in the non-round test liner.
When piston rings are produced, high manufacturing capability must be available to maintain the light tightness under operation, which is associated with significant costs. Even piston rings that are produced at a high manufacturing level must be subjected to a light tightness check at least occasionally, so as to establish in this way to what degree impermissible tolerances have arisen in the manufacturing process.